Varicella zoster virus (VZV) is a ubiquitous human alphaherpesvirus which is the infectious agent of two diseases, causing varicella (chickenpox) during primary infection and zoster (shingles) after reactivation from latency. A VZV vaccine is now in widespread use in children and may also be used in older adults in order to prevent zoster. In these contexts, it is essential for us to be able to understand the mechanisms of replication and virulence of this important human virus. During the past funding period we have identified the viral and cellular factors required for expression from a viral glycoprotein promoter and in doing so, have formulated a model for the mechanism of transactivation by the viral IE62 major transactivator. We have also assessed the roles of two other essential viral proteins (ORF 29 and IE63 proteins) in the regulation of VZV transcription. In this proposal we will refine our model of IE62 activation of the VZV gl promoter and examine the interaction of this protein with the ubiquitous cellular transcription factors Spl and USF. We will expand our work on VZV transcription into questions regarding latent gene expression using a novel VZV promoter (the ORF28/ORF29 promoter) which functions bidirectionally during lytic infection but unidirectionally in latency. Finally, we will examine the nature and the function of the interaction, identified during the last funding period, between the VZV IE62 and IE63 proteins and determine the function of the latter protein in VZV gene regulation. We will also examine the recently identified interaction between IE63 and the host RNA Polymerase II.